Prostaglandin A1 enhances c-fos expression and activating protein-1 activity.

Prostaglandin A1 (PGA1) increases heat shock element (HSE)-mediated transcription, thereby enhancing expression of HSE-bearing genes, including heat shock proteins. Because we recently found functional HSEs in the human and rodent c-fos promoters, we hypothesized that PGA1 might increase c-fos expression through the HSE. In this study, we revealed that PGA1 induces c-fos expression at least partly by increasing the binding between heat shock factor-1 and the HSE, and that PGA1 enhances activity of activating protein-1 (AP-1). Interestingly, so far as PGA, is present in the medium, AP-1-mediated transcription enhanced by PGA1 cannot be detected by the standard luciferase reporter gene assay. Instead, it can be detected by either checking luciferase mRNA levels in the presence of PGA1 or measuring luciferase activities just after removal of PGA1. These results showed that protein products of some stress-responsive genes can increase, not during the stressful condition, but immediately after recovery from stress.